Joel I. Klein, who presided over a radical reorganization of the New York City school system and drew praise and criticism for efforts to raise test scores and hold teachers accountable for them, resigned on Tuesday as chancellor after eight years in the job.

Mayor Michael R. Bloomberg appointed Cathleen P. Black, the chairwoman of Hearst Magazines, as Mr. Klein’s successor. Ms. Black will be the first woman to head the nation’s largest school system, with a $23 billion budget, 135,000 employees and one million students.

The decision was also noteworthy for the fact that Ms. Black, 66, has no educational background, in keeping with Mr. Bloomberg’s preference for executives from the business world. Because of that, she will need a waiver from the State Education Department; Mr. Klein, who had also been a media executive, was granted one when he took over, in 2002.

Mr. Klein, who had long planned to serve only through two mayoral terms, mulled the decision for the last few months and in the past week landed a job as an executive vice president at News Corporation.

Mr. Klein can make many claims about the successes of his tenure, including rising test scores and graduation rates, and the initial makings of an objective system to evaluate teachers and schools.

The truth of those claims, and their chances of having a lasting impact, will be debated in the months and years to come. His detractors argue that the test scores were inflated, that parents went unheeded and that teachers were derided and marginalized.

But the very robustness of the debate is testament to the fact that Mr. Klein did deliver on a central promise: to challenge orthodoxies, shake up the status quo and risk dislike in the name of progress.

“Did he stir things up?” Mr. Bloomberg said Tuesday. “You betcha. That was the job, and the great beneficiaries of that stirring were our children.”

Mr. Klein benefited from two historic conditions. He was the first chancellor appointed by the mayor and, as such, was answerable only to him, which gave him power and security. And he was part of — and widely considered a leader in — a national effort for greater accountability in public education shared across partisan lines.

Mr. Klein said he made a final decision to join News Corporation in the last week, a hire that puts a respected official with Democratic credentials — he was a top antitrust lawyer in President Bill Clinton’s Justice Department — in the executive suite at Rupert Murdoch’s conservative-leaning news media giant. A person familiar with the negotiations at News Corporation said Mr. Klein would be charged with pursuing “entrepreneurial ventures” that cater to the educational marketplace.

Despite the mayor’s praise and an apparent deep admiration for Mr. Klein, one former senior Bloomberg administration official, speaking on the condition of anonymity because he did not want to jeopardize his relationship with City Hall, said that many people in the mayor's bullpen were dissatisfied with Mr. Klein because “he’s been a political load for a while.”

One of the first concrete signs that Mr. Klein was not long for the job was the appointment of Sharon L. Greenberger as the Education Department’s chief operating officer in April — something that, according to the official, “was imposed over Joel’s objection.”

Mr. Klein will remain with the city until the end of the year to help with Ms. Black’s transition. In an interview Tuesday, Mr. Klein was clear about his accomplishments as chancellor. When he accepted the job, he was part of a rising educational reform movement that drew lessons from the corporate world, like increasing parent choice through innovations like charter schools, weakening traditional union protections like tenure and bringing numbers-based accountability to schools to evaluate and rank them and to improve teaching.

“It’s a much more performance-driven system, and a much more professional system, and less politicized than when I started,” Mr. Klein said.

With the mayor, he dismantled the unwieldy system of local control that created 32 school districts. Power was centralized in the central Department of Education office, relocated from Brooklyn next to City Hall to emphasize its importance. The city’s 1,000-plus principals were given unprecedented authority over large sections of their school budgets.

From nearly the day he started, Mr. Klein attacked the union’s core principles — seniority, tenure and a set pay scale. During the 2005 contract negotiations, he was able to end the long-standing practice of giving teachers with seniority the ability to select which schools to work in. But that decision created a pool of floating veteran teachers who received full salaries without a permanent position, costing the city tens of millions of dollars annually.

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Randi Weingarten, the president of the American Federation of Teachers and former head of the city’s teachers’ union, said that while she believed Mr. Klein was sincere in his efforts to improve student achievement, he had difficulty garnering support for his changes, both from educators as well as political leaders.

“Joel has a great intellect and did not suffer fools,” Ms. Weingarten said. “Sometimes what was lost was the ability to lead a great system in a way that you win the hearts and minds of the people who work in it and parents who send their kids there.”

In 2006, he introduced a system of A-to-F report cards, which rank most schools nearly exclusively on their progress on test scores. He chipped away at teacher pay based only on seniority, getting the union to agree to bonuses for schools that showed strong progress.

Some advocates and policy analysts said that Mr. Klein was a transformative force, turning the city’s public education system into something that people who had given up on it could believe in again. They said he welcomed talented educators to the back office and schools alike.

Joe Williams, executive director of Democrats for Education Reform, an advocacy group that supports charter schools and that has been often aligned with Mr. Klein, put it this way: “Joel Klein made public education sexy again.”

But Mr. Klein stumbled along the way, as when he adopted a reading curriculum of questionable efficacy early in his tenure only to reverse course after it did not produce good results.

Merryl Tisch, the chancellor of the State Board of Regents, frequently sparred with Mr. Klein — though largely privately — about his style of forcing change in the city. But Ms. Tisch said Mr. Klein successfully took a “dysfunctional system and gave it some management credibility.”

The city also benefited from Mr. Klein’s role as a national symbol of school reform, Ms. Tisch said, with private donors giving millions of dollars to help create new projects and experiments, like teacher performance bonuses and cash rewards for students who did well on exams.

“Joel will go down as one of the great urban educational reformers of this century,” Ms. Tisch said. “Not just because he fought hard fights, but he did it in New York City, which people had really written off.”

Yet, at every turn there was controversy. Schools were put under tremendous pressure to raise graduation rates or face closings. There was widespread concern that principals were inflating their numbers by granting credits to undeserving students.

“He is leaving us with a legacy of classroom overcrowding, communities fighting over co-located schools, kindergarten waiting lists, unreliable school grades based on bad data, substandard credit recovery programs and our children starved of art, music and science — all replaced with test prep,” said Leonie Haimson, the head of Class Size Matters, an advocacy group and a critic of Mr. Klein’s.

The opposition was further emboldened when the state announced this summer that the test scores on which Mr. Klein’s accountability system hinged were inflated because the exams had grown too easy to pass.

A correction brought test scores nearly back to the starting levels of the mayor’s tenure, replacing a narrative of historic gains with one of slow progress.

While Mr. Bloomberg and Mr. Klein said their achievements — opening 470 new schools, and raising graduation rates by 20 percent, for example — were beyond question, they acknowledged that there was much more to be done.

Asked whether he will be remembered as a divisive leader, Mr. Klein said, “I didn’t think you could make big changes to a $22 billion system — close down schools, hold people accountable, reward excellence — without pushback and controversy.”

“People will remember me differently,” he added. “They will remember me as a man who was committed to changing an educational system that was failing vast numbers of people. This was the most comprehensive school reform that has happened in this country.”

A version of this article appears in print on November 10, 2010, on Page A1 of the New York edition with the headline: KLEIN RESIGNING
AS CHANCELLOR
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